Thursday, October 30, 2008

Lesson 43: EPIRB

EPIRB Types

Class A - 121.5/243 MHZ. Float-free, automatically-activating, detectable by aircraft and satellite. Coverage is limited. An alert from this device to a rescue coordination center may be delayed 4 - 6 or more hours. This type of unit is no longer recommended.

Category II - 406/121.5 MHZ. Similar to Category I, except is manually activated. Some models are also water activated.

121.5/243 MHz EPIRB

These are the most common and least expensive type of EPIRB, designed to be detected by over-flying commercial or military aircraft (homing signals are picked up about 12 -15 miles). Satellites were designed to detect these EPIRBs, but are limited for the following reasons:

1. Satellite detection range is limited for these EPIRBs (satellites must be within line of sight of both the EPIRB and a ground terminal for detection to occur),

2. Frequency congestion in the band used by these devices cause a high satellite false alert rate (99.8%); consequently, confirmation is required before search and rescue forces can be deployed,

3. EPIRBs manufactured before October 1989 may have design or construction problems (e.g. some models will leak and cease operating when immersed in water), or may not be detectable by satellite. Such EPIRBs may no longer be sold,

4. Because of location ambiguities and frequency congestion in this band, two or more satellite passes are necessary to determine if the signal is from an EPIRB and to determine the location of the EPIRB, delaying rescue by an average of 4 to 6 hours. In some cases, a rescue can be delayed as long as 12 hours.

5. COSPAS-SARSAT is expected to cease detecting alerts on 121.5 MHz by 2008.On November 3, 2000, the National Oceanic and Atmospheric Administration (NOAA) announced that satellite processing 121.5/243 MHz emergency beacons will be terminated on February 1, 2009. Class A and B EPIRBs must be phased out by that date. The U.S. Coast Guard no longer recommends these EPIRBs be purchased.

406 MHz EPIRB

The 406 MHz EPIRB was designed to operate with satellites. The signal frequency (406 MHz) has been designated internationally for use only for distress. Other communications and interference, such as on 121.5 MHz, is not allowed on this frequency. Its signal allows a satellite local user terminal to accurately locate the EPIRB (much more accurately – within ½ mile), and identify the vessel (the signal is encoded with the vessel's identity) anywhere in the world (there is no range limitation). These devices are detectable not only by COSPAS-SARSAT satellites which are polar orbiting, but also by geostationary GOES weather satellites. EPIRBs detected by the GEOSTAR system, consisting of GOES and other geostationary satellites, send rescue authorities an instant alert, but without location information unless the EPIRB is equipped with an integral GPS receiver. EPIRBs detected by COSPAS-SARSAT (e.g. TIROS N) satellites provide rescue authorities location of distress, but location and sometimes alerting may be delayed as much as an hour or two. These EPIRBs also include a 121.5 MHz homing signal, allowing aircraft and rescue craft to quickly find the vessel in distress. These are the only type of EPIRB which must be certified by Coast Guard approved independent laboratories before they can be sold in the United States.

A new type of 406 MHz EPIRB, having an integral GPS navigation receiver, became available in 1998. This EPIRB will send accurate location as well as identification information to rescue authorities immediately upon activation through both geostationary (GEOSAR) and polar orbiting satellites. These types of EPIRB are the best you can buy (accuracy of position within 100 meters).